What Are The Models Saying This Winter? - NASA Model

This is a series of posts that I have made in previous years, in which I display a specific long range model and its prediction for the upcoming winter. Based on its success in past years, I have decided to kick off the multi-month series early, to give you an early heads up on the upcoming winter.

Today's model will be the NASA model.

The above image shows the NASA model's forecast of 200mb wind speed anomalies across the world, with 200mb pressure contour lines superimposed. We want to mainly pay attention to the contour lines for today's analysis, since it seems to be the easiest for many to decipher over the anomalies. If we look at North America, we see the contour lines arching up across the West Coast, likely indicative of the presence of high pressure/ridging. This ridging over the western portion of North America then leads to a depression in the contour lines, where cold air would funnel southward into the central and eastern portions of the continent. This cold air would be helped along south by that troughing/depression in the contour lines. In other words, going solely by this image from this single model, we would be looking at a very similar set-up as last winter, with warmth over the West and cold over the East.

If we look at the North American temperature forecast for December 2014, the same timeframe as the image above, we see a similar story to my analog package which I posted about earlier this week. We see cold weather present across the South US, with warmth prevailing over Canada and the North US. This temperature forecast looks very similar to a textbook El Nino event, which is expected to form this summer and result, possibly, in a temperature pattern similar to the one above for this winter.

Lastly, the temperature forecast from the NASA model, valid December 2014, confirms the idea of a textbook El Nino pattern. We can recognize this El Nino pattern by viewing the below-normal precipitation across the Great Lakes and Ohio Valley, with a very wet precipitation pattern swallowing the Southeast and East Coast. These two features are common during an El Nino winter, and may very well appear this winter. On the West Coast, in accordance with the ongoing drought, we see well-below-normal precipitation values extending from California to Washington. All in all, even though this is a long range forecast, this solution is indeed a plausible one from this model.

To summarize, the NASA model is predicting the following conditions to begin the winter of 2014-2015:
• Cool South US
• Warm North US
• Wet & Stormy East Coast, Dry West Coast
• Very similar to a typical El Nino pattern

Andrew

Potential Severe Weather Outbreak Projected for Mid-June

I'm seeing an increased probability for a severe weather event, potentially an outbreak, for the middle of June.

The image above shows a long range forecast of outgoing longwave radiation (OLR) anomalies over the equatorial region of the globe. In both of these images, the yellows represent positive OLR, or suppressed tropical convection, while the blues denote negative OLR, or enhanced tropical convection. We can see a strong active Madden-Julian Oscillation (MJO) signal on the bottom panel, with deep blues indicating abnormal convection occurring over southern India into the waters east of the subcontinent.

If we take a look at MJO composites for each phase, with blues once again defining enhanced convection and oranges signifying suppressed convection, it would seem that storms just east of India fit in best with a Phase 2 or 3 MJO event, seen on the left panels of this graphic above. Considering there has been a link observed between the MJO being in Phase 2 and violent tornado outbreaks occurring consequentially, there is reason to monitor this period for potential severe weather.

The image above shows projected 500mb height anomalies over the northern hemisphere. We can signify the blues with negative height anomalies, which indicate the presence of cooler and stormier weather, while reds denote positive height anomalies, which allow for warmer than normal and calm weather. In the image above, if we look towards the Bering Sea, we can see a very strong ridge of high pressure, seen by the splotch of red around the Aleutian Islands. This image is valid for May 13-14, and if we extrapolate it out 2-3 weeks using the Bering Sea Rule, we can expect high pressure and warm weather to appear in the East US. This extrapolated timeframe looks to fall around the time when this potential severe weather outbreak may strike, and the presence of strong high pressure migrating across the Eastern and Central US may amplify the potential for active weather.

Another device we can use to predict potentially active weather is this grid chart. The dates on the right display the date the forecast was made on, and the dates on the bottom legend indicate when this forecast is valid for. Warmer colors indicate the higher potential for severe weather. For instance, if I want to know the severe weather potential for May 20th on a forecast made on May 5th, I go up the legend on the left to find May 5th, then scroll on the corresponding horizontal line to find the May 20th box. In this case, we have been seeing elevated supercell composite values around the June 15-20 period for some time now, as the red box indicates. This is a long range forecast, but as you can see with severe weather events further to the left on the image, we can get a feel for severe weather potential a long way out, with more accurate forecasts usually coming a few days to a week prior to the event.

This potential event will be updated in coming days as more information becomes available.

Andrew

Summerlike Warmth Returns for First Days of June

I'm expecting summerlike warmth to come back for the first week or so of June.

The image above shows projected 500mb height anomalies over the northern hemisphere. We can signify the blues with negative height anomalies, which indicate the presence of cooler and stormier weather, while reds denote positive height anomalies, which allow for warmer than normal and calm weather. In the image above, if we look towards the Bering Sea, we can see a very strong ridge of high pressure, seen by the splotch of red around the Aleutian Islands. This image is valid for May 13-14, and if we extrapolate it out 2-3 weeks using the Bering Sea Rule, we can expect high pressure and warm weather to appear in the East US.

If we look at another 500mb height anomaly forecast graphic, this one valid on May 19th, we now see that our strong ridge has shifted west into the middle of the Bering Sea, with cooler, stormier weather now protruding into western Alaska. This tells us that we can expect warm temperatures in the first several days of June in the middle of the country, with cooler conditions along the Eastern Seaboard.

This warmth is supported by long range modelling of enhanced tropical convection around the central Pacific, which is typically associated with warmer than normal weather in the Central and East US in the May-June-July time period. The bottom panel in the graphic above demonstrates the enhanced convection (blue) present in the Central Pacific.

Andrew

May 21-25 Potential Storm System & Severe Weather

I'm analyzing the May 21-25 time period for a substantial storm system to bring cool weather and possibly some severe weather to the nation.

Tropical Tidbits

The image above shows projected 500mb height anomalies over the western Pacific. We can signify the blues with negative height anomalies, which indicate the presence of cooler and stormier weather, while reds denote positive height anomalies, which allow for warmer than normal and calm weather. Looking towards Japan on this forecast graphic, valid on May 15th, we see a substantial closed low approaching Japan, bringing in cooler than normal and unsettled weather for the area. If we utilize the Typhoon Rule, we can expect this storm system to impact the United States 6-10 days after this storm affects Japan, which would give us a May 21-25 time period.

Indications I am getting from this graphic tell me much of the United States may be impacted by this cooler than normal weather, and while I do believe severe weather is possible, I'm currently thinking any severe weather will be limited due to the lack of a powerful ridge advecting north over Japan prior to this closed low hitting the country.

Andrew

Preliminary 2014-2015 Winter Analogs

After some consideration, I've decided to create a set of analogs for the upcoming winter, using the same parameters that gave me such high success this past winter.

This post will be divided into two sections of analogs. We will begin with the analog years that matched any two of my five parameters I set forth for this winter.

The image above shows 500mb height anomalies across the northern hemisphere, where cool colors signify stormy and cool weather. Warm colors define the presence of warm and quiet weather. In this image, which shows 500mb height anomalies averaged out across these 9 analog winters, we see significant negative height anomalies across the western coast of North America, defining a textbook negative-Pacific North American index (PNA) pattern. In negative PNA patterns, low pressure dominates the West US, leading to warm weather in the Central and East US. We see ridging in southern Canada, spilling over into the northern United States. There is no clear blocking pattern over the Arctic Circle, meaning cold weather may be even more difficult to come by.

The temperature composite for these same analog years confirms this assumption. We see warm weather dominating the northern United States, maximized in the northern Plains. This sort of temperature pattern is typically associated with an El Nino, where we see warmer than normal weather in the Northern US, with cooler than normal weather in the South or West US.

The precipitation anomaly for these same years confirms the textbook El Nino set-up, as we see below normal precipitation affixed over the southern Ohio Valley down towards the Gulf Coast, and the Southwest US along the Gulf Coast experiencing above normal precipitation. This belt of above normal precipitation looks to be due to the abnormally active subtropical jet stream, another characteristic of an El Nino. We also see a stripe of wetter than normal conditions along the East Coast, which can be attributed to that El Nino-induced subtropical jet stream.

Let's now go over my preferred analogs, which match three of the five chosen parameters that fit the upcoming winter.

Looking at the 500mb height anomaly composite for the four years that match three of my five parameters, we see a much different story than we saw with the less-preferred analog set we just went over. We now see a well-defined blocking situation over the Arctic Circle, with strong positive height anomalies in Greenland and into Canada. This exemplifies the negative phases of the North Atlantic Oscillation (NAO) and the Arctic Oscillation (AO). The negative phases of these indexes both allow cold air to push into the United States, and the negative NAO permits the storm track to push north and threaten the East Coast with more coastal snowstorms.

The temperature composite for these four choice analog years is also a change from the other analog set. Rather than most of the United States being warmer than normal, the negative AO and NAO seem to influence temperatures to be well below normal across much of the nation, maximized in the southern Plains. We still see warmer than normal conditions in the upper Midwest, but these warm anomalies are more restricted than they were in the first analog set. Unfortunately, this could mean the second straight colder than normal winter, as I place more trust in this analog set than the one we first analyzed.

The precipitation composite for these four analog years shows a very stormy East Coast, with anomalies anywhere from 4 to 6 inches above normal, most enhanced in the Southeast. This precipitation pattern is still somewhat aligned with a typical El Nino pattern, though the dryness in the Southeast argues against this somewhat. I'm not as ready to accept this precipitation composite, considering how dominating the El Nino may be this winter, but as always, the analog set will be refined in coming months.

Andrew